1. Technical Field
The invention relates to a process for converting hydrogen sulfide to sulfur and hydrogen and, more specifically, to a process for reacting hydrogen sulfide gas with an anthraquinone, yielding sulfur and the corresponding anthrahydroquinone which is then converted back to the anthraquinone while releasing hydrogen gas.
2. Background Art
Many processes related to the petroleum industry generate gaseous by-products containing hydrogen sulfide, by itself or in a mixture with other gases, such as carbon dioxide. The by-product gas is generally oxidized to obtain sulfur. A common oxidation process is the Claus process, which oxidizes hydrogen sulfide directly with air to produce sulfur and water. One disadvantage of the Claus process is that it requires expensive pretreatment of the feed gas if carbon dioxide is present in high concentrations. At least a portion of the carbon dioxide must be removed from the by-product gas by pretreatment before oxidizing the hydrogen sulfide to maintain the efficiency of the oxidation process. Other shortcomings of the Claus process are that it operates at high temperatures, it requires exacting process control over the ratio of oxygen to hydrogen sulfide in the feed, and the annual maintenance costs for the Claus process are typically 20 percent of the initial capital investment. Finally, the sulfur content of Claus process tail gas released to the atmosphere is generally too high to meet stringent environmental regulations. To comply with these regulations, it is necessary to add more Claus stages and/or employ a separate tail gas clean-up process at great expense.
The art is rife with modified Claus processes and other hydrogen sulfide oxidation processes which attempt to overcome the deficiencies of the basic Claus process. U.S. Pat. No. 2,819,950 to Patton converts hydrogen sulfide to sulfur and hydrogen by means of a quinone having an oxidation potential of at least 0.2 volts, which excludes antraquinones. The reaction is carried out in an acidic solution, comprising water, aqueous alcohol or other hydrophilic solvent, to produce sulfur and hydroquinone. The hydroquinone is electrolyzed in solution to obtain quinone and hydrogen. U.S. Pat. No. 3,311,453 to Lusby converts hydrogen sulfide into sulfur and either hydrogen peroxide or oxygen by means of an anthraquinone disulfonate dissolved in water. U.S. Pat. No. 3,923,966 to Vaughan reacts hydrogen sulfide with an anthraquinone in an organic solvent in the presence of an amine catalyst to produce elemental sulfur and hydrogen peroxide.
The above-cited patents are all burdened by strict process controls needed to regenerate the hydroquinone. A simpler process is needed for treating hydrogen sulfide gas and, more specifically, a process is needed which decomposes a hydrogen sulfide gas by means of a quinone to recover sulfur and hydrogen in a simple, cost-effective and environmentally acceptable manner.